The invention relates to a process for the production of a coke from pitch, the coke having an aciculate texture, in which the coal-tar pitch is filtered at an elevated temperature and the filtrate is coked.
It has been proposed that a coke having an aciculate or needle-shaped texture be produced. Due to its specific properties and particularly due to small thermal volume expansion coefficient and a high degree of anisotropy, coke with an aciculate texture is suitable for the production of high quality graphite electrodes. Such an aciculate textured coke is obtained by means of the coking of a residue fraction which accumulates with thermal or catalytic cracking of crude oil fractions or which is produced from gas oil fractions or similar products of crude oil refining. A process for the production of coke from coal for pitch has similarly been proposed; such a process is especially interesting on account of the ready availability of the pitch with respect to both quantity and constant quality.
Certain pitches formed from coal tars are suitable starting materials for the production of an aciculate textured coke from pitch. (German Pat. No. 1,935,467, Offenlegungsschrift 2,025,071 and Auslegenschrift 116 504) Further suitable starting material including coal tar pitch freed of soot-like material (German Auslegenschriften 1,189,517 and 1,257,738). The soot portion of the coal-tar pitch should amount to less than 1%, preferably less than 0.3% of the weight of the pitch. For the separation of the sooty material, whose proportion is fixed like the quinoline-insoluble portions, and which detracts from the aciculate texture, separators, centrifuges or filters are used and, prior to such a separation step, the pitch is dissolved in a solvent such as absorption oil or anthracene oil. The separation of the quinoline-insoluble components can be done by means of filtration. (Auslegenschrift 2,064,695 and Offenlegungsschrift 2,159,862) The separation proceeds particularly smoothly if a certain low-boiling, aromatic compound, such as coal-tar oil, is added in large amounts to the pitch.
The so-purified pitch is coked with the aid of a special multistage low temperature carbonization process or by means of delayed coking in a delayed-coker.
The utility of the process will naturally be determined not only by the quality of the resulting coke from pitch, but also by the expenditure necessary for performing the coking. Especially suitable and advantageous are processes which make possible a
(1) simple separation and/or purification of the starting material, PA1 (2) a high yield of coke, and PA1 (3) production of a high quality coke in conventional coking ovens.
The yield of coke from starting materials obtained by distillation is, however, relatively small in coking under normal conditions. Larger quantities of coke will be obtained only by means of delayed coking under elevated pressure. Even bituminous coal-tar pitch, whose quinoline-insoluble components would separate by sedimentation, centrifugation, or filtration after addition of a solvent or a diluent, gives a poor yield of coke. This disadvantage can be avoided only with the employment of an additional process step for removing the solvent or the diluent, such as the step of distilling off the solvent.